backbone

noun

1. a central cohesive source of support and stability"faith is his anchor"
2. fortitude and determination"he didn't have the guts to try it"
3. the series of vertebrae forming the axis of the skeleton and protecting the spinal cord"the fall broke his back"
4. the part of a book's cover that encloses the inner side of the book's pages and that faces outward when the book is shelved"the title and author were printed on the spine of the book"
5. the part of a network that connects other networks together"the backbone is the part of a communication network that carries the heaviest traffic"